Frequently Asked Questions

Yes. Unlike competitor systems that require separate sensors for edge detection and line/contrast guiding, a single Roll-2-Roll® Sensor handles both functions. The same infrared sensor that detects physical material edges can also detect printed lines, coating edges, and contrast patterns. This dual capability reduces equipment cost and simplifies changeovers—operators don't need to swap sensors when switching between edge-guided and line-guided products.

Roll-2-Roll® Sensors achieve 0.0635 mm (0.0025 in) hardware resolution with repeatability greater than 99.9%. This precision is maintained across all material types without recalibration. For comparison, this resolution is approximately the thickness of a human hair. The sensors also feature linearity error of less than 0.25% across the full sensing range.

Sizing an unwind actuator requires more than knowing the total load weight. The key factors are:

1. Breakaway Force: The actuator must overcome static friction to start movement. This depends on the bearing type:
   • Low-friction linear rail bearings (coefficient ~0.01): A 10,000 lb load requires only ~100 lbf to start moving
   • Sliding shaft bearings (coefficient ~0.25): The same 10,000 lb load requires ~2,500 lbf
2. Acceleration Requirements: Higher acceleration for faster response requires proportionally more thrust
3. Safety Factor: Include 20-30% margin for binding, misalignment, and wear

Recommendation: Always use low-friction linear rail bearings. The cost savings on a smaller actuator typically exceeds the bearing cost difference, plus you get better dynamic response.

Roll-2-Roll Technologies RLA and BLA series actuators provide thrust from 50 lbf to 2,000 lbf, handling loads up to 30,000 lbs when paired with proper bearing systems.

Electronic guide point adjustment drastically simplifies product changeovers by eliminating the need for operators to physically reposition sensors when the web width changes. Instead of unlocking, moving, and re-locking a sensor hardware assembly, the operator simply changes the target position setting on the controller's touchscreen interface. Better yet with Roll-2-Roll® Controllers this can be completely automated with remote guidepoint adjustment either via industrial ethernet or digital I/O inputs.

Electronic guide point offers three specific benefits for product changeovers:

1. Elimination of Mechanical Adjustments & Safety Risks: In traditional "single edge guiding," a width change requires the sensor to be physically moved to the new edge location. This often forces operators to climb into the machine or reach into hazardous areas to adjust brackets. By using Roll-2-Roll® Sensor (e.g., 48mm to 960mm sensing window), the sensor remains fixed to the machine frame, and the "guide point" is moved electronically within the sensor's viewing window. This removes the operator from the machine, improving plant safety.
2. Reduction of Operator Error & Waste: Physical sensor repositioning is prone to human error. If an operator locks the sensor in the slightly wrong position, or if the sensor bracket is not rigid, the web will be aligned incorrectly, leading to immediate material waste. Electronic adjustment allows for precise, digital settings (e.g., 0.25mm increments with Roll-2-Roll® Controller) that are repeatable. Furthermore, these settings can be pre-programmed based on product codes, allowing for "recipe-based" changeovers where the guide point updates automatically without human intervention.
3. Removal of Mechanical Wear: Legacy systems sometimes use "sensor positioners" (electromechanical actuators that move the sensors) to automate this process. However, these introduce additional moving parts, maintenance requirements, and mechanical wear and tear. Electronic guide point adjustment achieves the same result mathematically using software and wide sensors, completely removing the need for mechanical sensor chasing mechanisms.

Roll-2-Roll® Web Guides can be set up in minutes, not hours. The sensors Auto-Setup function detects the web edge automatically without manual threshold adjustment, menu navigation, or stopping the machine. This is particularly valuable for converters running short production runs with frequent changeovers—there is no need to move sensors or recalibrate when switching materials or web widths.

Here are the primary advantages of center guiding:

Inherent Error Reduction (Averaging Effect)

The most distinct technical advantage of center guiding is that it averages the position of both web edges. By calculating the centerline based on inputs from two sensors (or one wide Roll-2-Roll® Sensor), the system inherently filters out edge imperfections.

• Fuzzy or Serrated Edges: If a web has rough, serrated edges (common in extrusion or nonwovens), a single-edge guide might oscillate as it tries to trace the jagged profile. Center guiding averages the left and right edge positions, smoothing out these variations and stabilizing the web.
• Wrinkles: Wrinkles effectively reduce the web width by pulling the edges inward. While a single-edge sensor might interpret a wrinkle as a position error and move the guide unnecessarily, center guiding sees the width change on both sides and maintains the centerline, reducing oscillation.
• Variable Opacity/Porosity: For materials that allow light to leak through (like nonwovens), legacy sensor readings can fluctuate. Center guiding significantly reduces the standard deviation of these errors compared to single-edge guiding. However, with Roll-2-Roll® Sensor this is not a problem.

Simplified Width Changeovers

In single-edge guiding, any change in web width requires the operator to physically move the sensor to the new edge location to maintain alignment. Center guiding eliminates this requirement for centered processes.

• No Sensor Repositioning: If the sensors are equidistant from the machine centerline and a wide sensor like Roll-2-Roll® Sensor is used, the web width can change (e.g., from a wide master roll to a narrower roll) without requiring the operator to move the sensors or adjust the guide point. The centerline remains constant relative to the machine. For legacy horseshoe/fork sensors it is important to ensure that width change does not snag the web. This is not an issue with Roll-2-Roll® Sensors since they are single sided. 
• Elimination of Mechanical Positioners: Traditional systems often required complex "sensor positioners" (motorized lead screws) to physically move sensors during width changes. Modern wide-sensor center guiding eliminates these moving parts, reducing mechanical wear and maintenance.

Simultaneous Process Monitoring

Because center guiding requires the detection of both web edges, it provides valuable secondary data that single-edge systems cannot:

• Width Measurement: The system can calculate and monitor the real-time width of the web while guiding it. This data can be used for quality control purposes.
• Web Break Detection: The presence of two sensors (or a wide field of view sensor) acts as a redundant web presence check. If the web breaks, the system knows immediately because it loses both edges, functioning as an inherent web break detector.

Process alignment

Center guiding is the standard requirement when downstream processes (such as printing, coating, or lamination) must be aligned to the middle of the machine rather than a specific edge. It ensures that despite variations in the incoming roll's width, the material remains centered relative to the tool or die or the print system.

Location and Function

• Terminal Guides: These are located at the very entry (unwind) and exit (rewind) of a roll-to-roll machine. Their purpose is to manage the master roll—either ensuring the web feeds correctly into the machine (unwind) or ensuring the roll winds up straight out of the machine (rewind).
• Intermediate Guides: These are located within the interior of the machine, typically just before a critical process such as printing, coating, laminating, or slitting. Their job is to shift the running web to align it for that specific downstream process.

Mechanism of Movement

• Terminal (Moving the Roll): Terminal guides function by moving the entire roll of material laterally. They typically utilize a "shifting stand" or "shifting base" on linear bearings to position the heavy unwind or rewind rolls.
• Intermediate (Moving the Web): Intermediate guides function by twisting or bending the web itself while the machine frame stays stationary. Mechanisms like Displacement Guides or Steering Guides displace the web by rotating or translating rollers over which the web passes.

Dynamics and Application

• Unwind vs. Rewind Dynamics:
  • Unwind Guides: Function as true guides. They shift the unwind stand to ensure the web enters the machine at a predetermined position.
  • Rewind Guides: Function as chasing systems. They do not control the web's lateral position; instead, the rewind stand moves to align the winding roll with the incoming web edge to ensure a straight roll.
• Intermediate Dynamics: Most intermediate guides (specifically Displacement and Steering guides) rely on the Normal Entry Rule, which states that a web will align itself perpendicular to the axis of the roller it is approaching.

Sensor Placement

• Terminal Guides:
  • Unwind: The sensor must be fixed to the machine frame (it does not move with the stand) and positioned immediately downstream of the shifting idler,.
  • Rewind: The sensor must be attached to the moving rewind stand so it moves with the carriage to "chase" the web.
• Intermediate Guides: The sensor is always located in the exit span (the span immediately following the guide roller) and moves with the web, not the guide mechanism. It should be placed as close to the exit roller as possible.

Actuator Requirements

• Terminal Guides: Because they often move heavy master rolls (potentially thousands of pounds), they typically require high-thrust actuators and robust mechanical rigidity to avoid resonance.
• Intermediate Guides: These move lighter guide frames and rollers, focusing more on dynamic response and low friction than raw thrust.

Fork sensor collision occurs when the web width increases unexpectedly (due to material variation, tension changes, or process adjustments) and the expanding web physically contacts the fork-style sensor assembly. This causes web damage (scratches, contamination), sensor damage (misalignment or breakage), emergency line stops, and material waste. Roll-2-Roll® Sensors avoids this entirely by using wide one-sided sensor mounted outside the web path—even when web width increases dramatically, there is no physical sensor in the way.

Roll-2-Roll® Sensors eliminate the need for mechanical sensor positioners—motorized assemblies that move sensors to chase edge positions. Traditional center guiding requires sensor positioners because narrow sensors cannot see both edges when web width changes. These positioners introduce motors, lead screws, and sliding brackets that jam, wear out, and require maintenance. Roll-2-Roll® Sensors have wide fields of view (48-960 mm) allowing them to track width variations electronically without moving parts, eliminating a major category of mechanical failures and maintenance.

Mechanical Master/Slave (legacy): The Master sensor is mounted on a motorized slide that physically chases the web position. The Slave sensor is mechanically linked to move the same distance. This creates wear parts, lag, and "loop within a loop" tuning problems.

Electronic Master/Slave (Roll-2-Roll Technologies): Both sensors connect to a single controller. The controller reads the Master position and electronically adjusts the Slave guide point in real-time—no physical sensor movement. This eliminates mechanical lag, wear parts, and tuning instability.

The electronic approach also enables capabilities impossible with mechanical systems, such as centerline matching between webs of different widths.

Preventing Loss of Focus

In line or contrast guiding, optical sensors or cameras are used to track a printed feature or line. These sensors require a stable focal distance to operate accurately. However, as the web guide mechanism actuates (moves back and forth), it creates a "twisting" effect in the web span, causing the web plane to shift closer to or further away from the sensor. This movement, known as pass line variation, can cause the sensor to lose focus, affecting the amount of light reflected back and disrupting the "teaching" or tracking of the feature.

Web Stabilization

The dead bar acts as a stabilizer. By wrapping the web over this bar, the web is forced to maintain a fixed distance relative to the sensor, regardless of the guide's movement or the twisting happening in the span. The sensor is then mounted specifically to "look" at the web directly over this dead bar.

Installation Specifications

• Mounting: The sensor should be installed to view the web while it is in contact with the dead bar.
• Wrap Angle: To prevent the dead bar from influencing the lateral dynamics of the web too heavily (which could cause drag or steering issues), the wrap angle should be kept small.
  • Dead Bar (Stationary): Maximum of 5 degrees wrap.
  • Idler/Backup Roller (Rotating): Up to 15 degrees wrap.

Application in Terminal Guides

For unwind or rewind applications where line guiding is required, the setup is slightly different to accommodate the moving stands:

• Unwind: A shifting idler or dead bar must move with the unwind stand to support the web, but the sensor must be fixed to the machine frame,.
• Rewind: The sensor moves with the rewind stand (chasing the web), and a fixed idler or dead bar is placed in the span just before the rewind.

Roll-2-Roll® Sensors use patented fiber-optic technology based on light scattering rather than light blocking. This means they detect the physical presence of the web edge regardless of optical properties.

Materials that work:

• Clear and transparent films
• Porous nonwovens
• Metallic foils
• Glass
• Mesh and perforated materials
• Rubber and textiles
• Carbon fiber
• Abrasive materials

The only challenging material is matte carbon black that absorbs infrared light without reflection—and even this can be addressed by angling the light source.

• Manual Sensor Respositioning: If the web is guided to the centerline position using single-edge methods, the sensor must be moved for every width change, increasing setup time and complexity. 
• Possible Operator Error: Physical repositioning relies on the operator to correctly locate the sensor relative to the machine and securely lock it in position. Mistakes here can lead to misalignment. 
• Fork Sensor Issues: Conventional fork stype sensors could snag the web material if the sensor is not moved before the width change. And even after width change the sensor needs to be repositioned to ensure that the web is inbetween the two sensing arms. 

Legacy systems attempt to solve this with mechanical sensor positioners (moving sensor center guides or even moving a single sensor), but these introduce additional mechanical wear and tear. Roll-2-Roll® Sensors solves this with sensors and adjusting the electronic guide point using Roll-2-Roll® Controller, eliminating the need to physically move the sensor when the web width changes. 

More importantly the Roll-2-Roll® Sensors are single sided completely eliminating the possibility of snag or web threading issues during width change over. 

Intermediate Guides (Displacement & Steering Guides)

For web guides located within the machine process, the sensor must be placed in the exit span (the web span immediately following the guide roller).

• The "1/3rd Rule": The sensor should be located in the upper 1/3rd (or at least the first half) of the exit span.
• Avoid Delays: Placing the sensor too far downstream or in the next span creates time phase lag (delay). This causes the guide to continue moving even after the error is corrected, leading to system instability and oscillation.
• Steering Guides: The sensor should be placed as close as possible to the exit roller within the exit span.

Terminal Guides (Unwind & Rewind)

Because terminal guides move the entire roll stand, the sensor mounting acts differently:

• Unwind Guides: The sensor must be fixed to the machine frame (it does not move with the stand). It should be placed immediately downstream of the last shifting idler on the unwind stand.
• Rewind Guides: The sensor must be attached to the moving rewind stand so it moves with the carriage (chasing the web). It should sense the web position just ahead of the last fixed idler using a mechanical arm connected to the rewind stand. Ideally, this is as close to the winder as possible to minimize instability caused by mechanical arm stiffness.

Plane Change Considerations

If the motion of the web guide causes the web plane to twist or shift significantly (common in line guiding), it can cause focus issues for optical sensors. In these cases, a backup roller or dead bar should be installed, and the sensor should be mounted to look at the web directly over this stabilizer to maintain a constant focal distance. 

Roll-2-Roll® Sensors use patented fiber-optic technology with adaptive edge detection algorithms. Unlike ultrasonic sensors that measure sound reflection (affected by material density and porosity) or simple infrared sensors that require threshold adjustment,  [rr sesors] use spatial light filtering to detect edges regardless of material properties. The sensor automatically adapts to different reflectivity, transparency, and surface characteristics—whether running clear films, opaque substrates, metallic foils, or porous nonwovens.